Spring guide for mechanical rectifier contacts



Spt. 9, 1958 J. PARSTORFER SPRING GUIDE FOR MECHANICAL RECTIFIER CONTACTS 3 Sheets-Sheet 1 Filed June 22, 1954 INVENTOR.

.70/9/1 f/MSTOfi/ZW P 1958 J. PARSTORFER 2,851,561

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JOHN PARSTORFER Sept. 9, 1958 J. PARSTORFER SPRING GUIDE FOR MECHANICAL RECTIFIER CONTACTS 3 Sheets-Sheet 3 Filed June .22, 1954 INVENTOR. fol/Al 70/3/22 W ?/i /rrd/a/v9o' United States Patent "cc SPRING GUIDE FOR MECHANICAL RECTIFIER CONTACTS John Parstorfer, Philadelphia, Pa. assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Application June 22, 1954, Serial No. 438,465

12 Claims. (Cl. 200-166) My invention relates to guide means for the cooperating contacts of a mechanical rectifier and is more particularly directed to a novel guide which has good guiding characteristics and long life.

The guide contact arrangement of my invention may be applied to the type of mechanical rectifier disclosed in U. S. Patent 2,759,128, issued August 14, 1956, U. S. Patent 2,759,141, issued August 14, 1956, assigned to the assignee of the instant case.

A mechanical rectifier produces direct current by making bridging contact between a proper phase of an A.-C. system and the associated D.-C. system during the timer interval the particular phase of the A.-C. system is capable of delivering energy in the desired direction and breaking the bridging contact when the A.C. phase reverses its voltage in relationship to the D.-C. voltage. This operation is performed sequentially and repeatedly in synchronism with the A.-C. frequency.

Mechanical rectifiers utilize a commutating reactor, which is a non-linear or saturable type reactor, to step the current when it passes through zero value, This operation is fully described in U. S. Patent 2,693,569, issued November 2, 1954. During the period of each stepping operation either contact engagement or disengagement must be completed. Hence, in a three phase mechanical rectifier conversion unit it is necessary for the contact assembly to make and break the circuit 216,000 .times per hour in a 60 cycle system.

It is therefore, apparent that contact assembly is a vital component of the conversion unit and must be designed .to contribute directly to the quality of conversion performance. Co-pending application Serial No. 307,024, :filed August 29, 1952, is directed to the contact time adjustment for the contact assembly and the instant application is directed to a guide means for the movable .bridging contact.

The make and break of the contact assembly is designed to occur during the stepping length of the current so that contact engagement and disengagement will occur during zero current flow. However, even though there usually is an absence of current at the time of making and breaking connections the contact assembly must carry 5,000 amperes and serve through 1,866,000,000 operations for a 360 day period. Improper contact time adjustment for a short period of time may result in contact pitting, burning and corrosion.

The cooperating contacts of a mechanical rectifier are contained in a removable and replaceable contact block in which a helical spring is mounted for biasing the bridging contact into engaged or make position with the stationary contacts.

In the prior art arrangements the helical spring functions as both a biasing means and a guide means. However, this arrangement has disadvantages in that during the period of contact disengagement or break the helical spring may cause the bridging movable contact to rotate about its longitudinal axis, move or slide in a transverse direction with respect to the longitudinal axis or tilt the Patented Sept. 0, 1958 contact about its plane so that it is tilted with respect to the stationary contacts. These undesirable movements of the bridging contact cause the creation of silver dust at v the time of contact make and result in overheating when the cooperating contacts are not symmetrical or parallel.

My invention increases the mechanical life of the mating silver contacts by preventing the formation of silver dust. In unguided contacts silver dust is created by the minute relative motion between mating contact surfaces, e. g. if the two mating contact surfaces are permitted to skid or slide or rotate even as litle as .001" then in three months operation of the contacts the total distance traveled will be more than 30 miles and that amount of skidding of the mating surfaces under the action of the contact spring will generate much silver dust due to abrasions between the mating surfaces.

The silver dust is undesirable for two reasons; first, it reduces the mechanical life of the contacts, and, second, the silver dust may form into a chain, one end of which might adhere to the moving contact when it opens while the other end might rest on the stationary contact. Should this be the case, the metallic connection between the moving contact and the stationary contact will not be broken when it is supposed to be and a strong current will flow through the silver chain during the non-conducting cycle of the contacts resulting in a backfire which will shut the machine down and cause damage to the backfiring contacts as well as adjacent contacts.

Even if no actual backfire occurs due to the building up of the chain of silver dust, the individual grains of silver dust have a disturbing influence on contact life. If one silver grain is present between the moving and stationary contacts and we consider that the moving contacts are opening, then the small amount of residual current which flows through the contact on opening will flow through this single grain of silver dust. As the silver dust has a very small cross sectional area, this grain under the influence of current flowing through it, reaches a White hot temperature and will in turn become welded to one of the mating surfaces. This process keeps on and eventually the contact surfaces will be very rough, con sisting of projections on one contact and mating crevices on the other. If the projections and the crevices always match no great harm is done; but if upon opening of the contacts a sliding motion takes place, then the projection will rub against the sides of the crevices, and, therefore, prolong the contact time. This prolongation can be so severe that the contact breaks too late in the cycle and again a backfire will result.

Furthermore, any pittings or erosion of the contacts usually occurs in the form of a protrusion on one contact and a mating crevice on the other contact. If the bridging contact is rotated with respect to the stationary contact (i. e. about the longitudinal axis of the helical spring) a protrusion on one of the contacts will subsequently engage a fiat on its cooperating contact rather than its mating crevice.

Hence, the time of contact engagement will be considerably altered. That is, since the push rod which controls the movement of the movable contact travels at a speed of 27 inches per second, a one-thousandth of an inch change in the thickness of the cooperating contacts will cause an 0.8 electrical degree change in the timing.

Accordingly, it is a distinct disadvantage to allow contact rotation even if the contacts remain parallel and symmetrical since a considerable change in timing may result.

With my novel device, I provide a guide device for the contact block assembly so that the helical spring functions only to bias the contacts and a separate guide means performs the function of guiding the bridging contact so that it will not rotate, tilt or slide.

Experiments have shown that flat solid guide means may not prevent tilting, do not have a long life due to undue tension stresses resulting from elongation or deflection and cannot be positioned in a compact area. However, I have provided a novel flat wing shaped guide member which overcomes not only all of the disadvantages of the prior art, but also all of the disadvantages encountered with aflat solid guide means. p '7' My novel guide means has good guiding ability in all directions, large deflection, insulating properties, heat resistance, low natural frequency and thus resistanceto shock, long life against fatigue and'breakage, and small space requirement to avoid interference'with other components of the mechanism.

Accordingly, it is a primary object of my invention to provide a novel guide means for a'bridging contact which prevents rotation, tilting and sliding of the contact.

Another object of my invention is the provision of a guidemember which has a large deflection and very fatigue with resulting long life.

Another object of my invention is to provide a novel reentrant guide member which will prevent contact wear and tear by guiding the bridging contact into the same position during each cycle.

Another object of my invention is the provision of a novel guide unit which will always maintain the same positional relationship of the cooperating contacts, so that if irregular contact surfaces develop contact closure time is not affected in an amount to cause failure.

Still another object of my invention is to provide a guide member which can be fitted into a limited smallarea, have insulating characteristics, have good guiding characteristics and long life.

Another object of my invention is the provision of a novel configuration for a guide member so that minimum tension stresses are set up even though the unit is capable of large deflection.

Another object of my invention is to provide a guide member in which the distance from the moving point to the bending point is larger than the distance from the moving point to the fixed point. i

Another object of my invention is the provision of a guide means which can be used on both high and low frequency oscillating devices such as a loud speaker armature and short circuiter, respectively. My novel guide member has no inherent limitations as to size and has universal application.

These and other objects of my invention will be apparent from the following description when taken in connection with the drawingsin which: i 4

Figure l is a schema'tic' fwire diagram of a mechanical rectifier to which my novel guided contact arrangement can be applied.

Figure 2 is a perspective view of the mechanical operating mechanism and illustrating the manner in which my novel guided contacts are synchronously driven into engaged and disengaged position.

Figure 3 is a cross sectional view of a contact block assembly and illustrates my novel guided meansassociated with the bridging contact.

Figure 4 is a top view illustrating the configuration of my novel two way slotted flexible guided means.

Figure 5 is a top view of a two .way slotted flexible guide means and illustrates an alternate design utilizing the principles incorporated .in the embodiment of Figure 4.

Figure 5A is a cross sectional view of the guide unit illustrated in Figure 5 when it is operative in a contact structure as illustrated in Figures 2 and 3. This figure illustrates the neutral position, the extreme upper posi tion, and "the extreme lower position of the moving contact and guide means.

Figure 5B is a schematic side view illustration similar to Figure 5A illustratingv sequence of movement of the 4 various points of my novel guide means as it moves through a complete cycle.

Figure 6 is a top view of a four way wing slotted flexible guide means. This figure illustrates a guide unit utilizing the principles of the two way guide of Figures 4 and 5 so that guiding characteristics are achieved in four directions.

Figure 7 is a top view of a four way wing shaped guide means and illustrates a second embodiment of Figure 6.

Figure 8 is a cross sectional view of a contact block illustrating the manner in which my novel guide means can be utilized in connection with a guide rod for the bridging contact.

In Figure 1 the source of alternating current is derived from the A.-C. voltage source which energized the conductors 10, passes through the circuit breaker 11 to the step down transformer 12. The current is subsequently passed through commutating reactor 13 to step the current for commutating purposes as set forth in U. Patent 2,693,569, issued November 2, i954. The construction of the commutating reactor is described in U. S. Patent 2,759,128, issued August 14, 1956.

The current then passes through the disconnect switches 14 to the contact assemblies and 71 which form the subject matter of the instant application. The contact assemblies 70 and 71, which are sequentially operated and are in synchronism with the frequency of the source, are connected to the alternating source buses 10A, B and C to the direct current load buses 29 and 21.

i For purposes of simplification, I have shown in Figure 2 themechanical switching arrangement which is utilized for phase A, it being understood that the switching apparatus for phases B and C are identical in construction. This figure illustrates the manner in which my novel guide contact assembly is mechanically driven for synchronous engagement and disengagement of the contacts.

A synchronous motor 40 drives the shaft 41 which in turn operates the eccentric member 43 to thereby aiternately drive the push rods 46 and 47 upwardly through the bell cranks 44. A detailed explanation of the construction of the adjustment and control by means 48 is set forth in co-pending application Serial No. 307,024, filed August 29, 1952.

The upward movement of thepush rod 47 will urge the disc shaped bridging contact 3 1 upward against the bias of the helical spring 51 and thereby disengage it from engagement with the stationary A.-C. contact 28 and the positive D.-C. stationary contact 26. During this period of time the push rod 46 is in its lowermost position and hence the bridging contact associated with the structure 71 is biased into contact engagement by the helical spring associated with the contact assembly 71.

On the next half cycle, the position of the push rods 46 and 47 will be reversed by the bell crank 44 so that the push rod 47 will be in its lowermost position and the push rod 46 will be in its uppermost position. Hence, at this time the bridging contact 31 associated with the contact block assembly 70 will be in engagement with its associated stationary contacts 28 and 26 and the bridging contact associated with the contact block assembly 71 will be disengaged from its associated contacts 25 and 27.

Thus, throughout a complete cycle of operation the bridging contacts-will also complete a mechanical cycle of operation.

My invention is directed to a novel guide means for the bridging contact such as 31 to prevent rotation, sliding and tilting thereof during its' cycle of operation.

In Figure 3 Ihave shown a cross sectional view of a contact block assembly such as 70 illustrating the manner in which the guide means is positioned with respect thereto. The contact assembly 70 is comprised of a housing 50, which has a box like form and is preferably made of an insulating material. A helical spring 51 is mounted within the housing between the bridging contact 31 and the spacer 52. The spacer 52 is provided to obtain the proper tension of the helical biasing spring 51 and may be made of brass.

The stationary contacts 26 and 28 are secured to the housing by means of assembly screws 53 which are passed through an opening 54 within the housing 50'which communicates with the upper end thereof, as best seen in Figure 2. Each of the four openings 54 receive an assembly screw 53.

The housing 50 is provided with a lower portion 55 and 56 which serves as a guide spacer for the guide means 60. As best seen in Figures 4 and 5 the guide means 60 is provided with holes 57 which communicate with the openings 54 when the guide means is positioned between the guide spacers 55 and the housing 50.

The stationary contacts 26 and 28 are each provided with two sets of threaded openings to receive the threaded ends of the assembly screws 53. Hence, when the contact block 70 is assembled as illustrated in Figure 3 the assembly screws 53 serve to position the guide means 60, hold and maintain the guide spacers 55 and 56 and hold and maintain the stationary contacts 26 and 28. Thus, the arrangement provides for supporting means at four fixed supports for the guide of Figure 3 and two fixed supports for the guide of Figure 5.

In the positions illustrated in Figure 3, the bridging contact 31 is in engagement with its associated stationary contacts 26 and 28. However, as noted in connection with the description of Figure 2, the bridging contact 31 is driven by means of the push rod 47 upwardly against the bias of the helical spring 51 to thereby disengage the bridging contact 31 from its stationary contact 26 and 28.

My invention is directed to the novel flexible slotted guide means 60, on which the bridging contact 31 is mounted in order to ensure that the bridging contact will not rotate, tilt or slide with respect to the stationary contacts 26 and 28 during its cycle of operation.

The guide means 60 is preferably made of an insulating material so that the movable contact 31 does not have a conducting path through the assembly screw 54 to the stationary contacts 26 and 28 when the cooperating contacts are in the disengaged position. The guide means 66 should therefore also have low hydroscopic distortion and be resistant to oil. All of these properties can be obtained by making the guide member of melamine. Thus, the insulated guide member 60 will serve a mechanical and electrical function within the contact assembly structure 70. That is, it will serve as a guide means for the movable contact 31 and also prevent a conducting path from existing between the movable contact 31 and the stationary contacts 26 and 28 through the assembly screw 53 when the push rod has moved the bridging contact to its disengaged position.

Furthermore, it is preferable to make the guiding member 65 of a woven glass fibre insulating material so that any tension stresses which may be built up will damage only the fibre at the location of the stress and will not split the remainder of the material. Furthermore, by making the guide member 60 of an insulating material rather than, for example, a metallic member, it is possible to substantially reduce possible harmonic vibrations of the guide member so that it will oscillate only with the frequency imparted thereto due to the vertical oscillation of the push rod assembly. Hence, the guide memher will also be insensitive to shock.

The movable contact 31 is provided with a reduced cross section upwardly extending portion 32 which passes through an opening 61 in the center of the flexible guide means 6!). As illustrated the contact opening 61 preferably provided with a flat portion which will serve as a key so that the movable contact 31 can be mounted on the guide means 60 in only one position.

The guide means 60 is provided with elongated slots 6 62 and 63 which straddle either the moving point 61, as seen in Figure 4, or the stationary points 57 as seen in Figure 5.

It will be noted that the elongated slots 62 and 63 are interposed between the moving point 61 and the stationary points 57 in both embodiments to mechanically isolate one from the other. With this novel configuration I am able to achieve. a desirable guide which is hereinafter more fully described. In addition the guide unit is provided with four openings 57 to receive the assembly screws 53 as noted above.

The re-entrant shaped configuration of Figures 5 and 4 permits a novel relationship of points within the guide member 60 so that a large deflection of the flexible guide member can be achieved while maintaining both good guide characteristics when the guide is in its neutral po sition and achieve long life of the guide member by substantially reducing tension stresses. As noted, the guide member 60 is secured between the housing 50 and the guide spacers 55 and 56. The areas 58 and 59 of the guide member 60 which remains stationary at the fixed supports due to its being sandwiched between the guide spacers and the housing 50 is illustrated by diagonal lines extending up and to the right.

The portion of the guide member 60 which is movable with the bridging contact 31 is illustrated by diagonal lines extending upward and to the left, and is identified by the numeral 49. The guide member 60 will have a bending or flexing line which is indicated by the dotted lines 64 and 65. The novel wing shaped configuration permits the distance Y between the moving point or area 49 to the stationary point or area 58, 59 to be less than the distance X from the moving point or area 49 to the flexing or bending point 64, 65. This dimensional relationship permits the flexing or bending portion 64, 65 to follow a curved path as clearly seen in Figures 5A and 53, as the guide means 60 is deflected throughout a cycle so that the efiective length between the flexing line 64 and the flexing line 65 will remain constant to thereby reduce,.to an absolute minimum, the tension stresses which may be set up within the guide member 60.

Thus, for example, as seen in Figure 5A and 5B the flexing line 64 will following the curved path 66 and the flexing line 65 will follow the curved path 67. The extreme right and left hand free ends 68, 69 of the guide member 60 will remain parallel as the guide member moves through its complete cycle, but will follow a curved path similar to 66 and 67.

Figure 5A illustrates the extreme upward, the extreme lower and the neutral positions of the guidemember 60 and as clearly seen in this figure the flexing lines 64 and 65 will respectively follow the curve paths 66 and 67 so that the effective length between these two lines will remain constant and thereby substantially reducing tension stresses within the flat guide member 60. In the embodig ment of Figure 5 the guide 60 is also provided with slots 72 and 73 to facilitate the curved movement and further reduce stress.

Figure 5B illustrates the plurality of positions that the guide member 60 will transverse as it moves through a complete cycle. As clearly. seen in the superimposed views of both Figures 5A and 5B my novel wing shaped configuration wherein the distance of the moving point 49 and the flexing point 64, 65, permits the flexing point to move in the above noted curved path thereby permitting large deflection without setting up stresses within the guide member 60.

It will be further noted that in the two way guide structure of Figures 4 and 5 wherein a wing shaped configuration is used, I am not only able to substantially reduce the tension stresses with the guide member but I am also able to confine this unit to a relatively compact area due to the novel re-entrant configuration.

It will be apparent that any number of wing shaped configurations can be designed with the principles of my invention wherein the above noted dimensional relationships are maintained. With this wing shaped configuration rotation and sliding of the moving contact is prevented, so that the guided member 31 will have straight line motion.

In the embodiments of both Figures 4 and 5 the guide member 60 is referred to as a two way guide. That is, the guide member will prevent the tilting of the movable contact 31 along the vertical axis in the plane of the guide means as seen in Figures 4 and 5. However, it may not prevent the tilting of the movable contacts along the horizontal axis in the plane of the guide means as shown in Figures 4 and 5. Although the guide means of Figures 4 and 5 is symmetrical about both the horizontal and vertical axes in the plane of the guide member, it is not identical about both axes.

In Figures 6 and 7, I have shown a modification of the novel guide means along the principles of my novel guide member shown in Figures 4 and 5 and incorporated in such a manner that the unit is symmetrical and identical about the horizontal and vertical axes in the plane of the guide means and hence, prevent tilting in all directions as well as preventing rotation and sliding.

In the illustrations of Figures 6 and 7 I have used the same numerals and notations as used in Figures 4 and 5 to identify similar parts. Thus, the heretofore described dimensional relationship is still maintained within the four way double Wing guide 80 of Figures 6 and 7. That is, the distance from the moving point to the stationary point is less than the distance from the moving point and the bending point.

A motion picture of the operation of the four way double wing guide 80 of Figures 6 and 7 have a view in both the horizontal and vertical axes in the plane of the guide member as seen in Figures 6 and 7 similar to that seen in Figures 5A and 5B for the guide of Figures 4 and 5.

With my novel arrangement of the four way guide it is possible to eliminate tilting about any of the axes of the guide means. Furthermore, since the device is identical and symmetrical about both axes there will be no tension stresses set up within the guide member since all of the bending points will be able to follow a curved path, thereby enabling the effective length of the guide member to remain constant throughout the entire cycle of operation as heretofore described for the two way guide member, in connection with the Figures 5A and 5B.

Thus, not only will the tension stresses or forces within the guide member be substantially reduced, but also due to the symmetrical and identical configuration about both axes there will be an equal distribution of stresses which may exist, thereby substantially increasing the life of the contact means while obtaining both large deflection and good guiding ability when the' unit is in its neutral position.

Heretofore, I have described by novel guide means in connection with the bridging contact of a mechanical rectifier. However, it will be apparent to those skilled in the art that my novel guide member can be applied to any oscillating member which requires guiding to prevent rotation, sliding or tilting of the oscillating member during its cycle of operation. By way of example, I have shown in Figure 8 a typical application of my novel guide means wherein the unit is utilized to guide the rod 90 of oscillating bridging contact, and, furthermore, illustrates the manner in which the guide means incorporating my novel design can be combined to operate effectively on members having a substantial length. As seen in Figure 8 the bridging contact 31 has a rod 99 secured to one end thereof.

The entire unit is housed within the housing 50 which is provided with a barrier 91 and a central opening therein to receive the rod 90. One end of the rod 90 is secured to the bridging contact 31 and the guide member 82, the guide member may be any combination of two or four way guides such as shown in Figures 4, 5, 6 and 7. If two way guides are used for both 81 and 82, they may be positioned criss-cross to prevent tilting in either direction. A helical spring 51 is lodged between the guide member 82 and the barrier 91 to thereby bias the bridging contact 31 into electrical engagement with the stationary contacts 26 and 28. As noted, the guide means and 81 may be a two way guide such as shown in Figures 4 and 5 or may be a four way guide as shown in Figures 6 and 7, or any combination. However, the principles of operation and construction is identical to that heretofore described in connection with these figures.

Accordingly, the rod will be properly guided so that it will not rotate about its vertical axis, will not tilt about its vertical axis nor will it be able to slide in a plane parallel to its vertical axis. Since the bridging contact 31 is rigidly secured to one end thereof the bridging contact will be restricted to straight line oscillatory movement and remain in register and parallel to the stationary contacts 26 and 28, at all times.

Thus, Figure 8 illustrates a typical application of my novel guide means for oscillating units such as rod 90 which may have a substantial length wherein two or more guide members can be coordinated to derive the desired results.

Accordingly, in both the arrangement of Figure 3 and in the arrangement of Figure 8 the guided bridging contact will be moved into the same position with respect to the stationary contacts on each closing operation so that any material transfer will be substantially reduced and furthermore if irregularities on the contact surface should develop a contact closure time will not be altered, since the protrusions and crevices on the cooperating parts will continue to mate with each other due to the fact that the positional relationship of the cooperating contacts is not changed.

In the foregoing, I have described my invention only in connection with'the preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein, but only by the appending claims.

I claim:

1'. In combination, a first contact, a second contact movable into and out of engagement with said first contact, biasing means for biasing said second contact into engagement with said first contact, means for operating said second contact out of engagement with said first contact against the action of said biasing means, a flexible member consisting of three sections separated by two slots in said member extending along said member, a support for each outer section; each support being intermediate the ends of the associated section whereby, as said second contact moves from engaged to disengaged position, it moves in a straight line while maintaining the length of the member from the contact to each support constant.

2. In combination, a first contact, a second contact movable into and out of engagement with said first contact, biasing means for biasing said second contact into engagement with said first contact, means for operating said second contact out of engagement with said first contact against the action of said biasing means, a single flexible member carrying said second contact, a first and second fixed support for said member, said member llflV- ing its ends free to move in an arcuate path whereby said contact moves in a straight line while maintaining constant the length along said member from said contact to said supports.

3. In combination, a first contact, a second contact movable into and out of engagement with said first contact, biasing means for biasing said second contact into engagement with said first contact, means for operating said second contact out of engagement with said first contact against the action of said biasing means, a flexible supporting member, a slot in said member forming therein a first and second section, a fixed support for said member intermediate to the ends thereof, said second contact being secured intermediate to the ends of the second section, the ends of said member being free to move in an arcuate path as said contact moves from ento disengaged position whereby said contact movement is in a straight line and the length of the member from said contact along said member to said support remains constant.

4. In combination, a first contact, a second contact movable into and out of engagement with said first contact, biasing means for biasing said second contact into engagement with said first contact, means for operating said second contact out of engagement with said first contact against the action of said biasing means, a flexible supporting member, a slot in said member forming therein a first and second section, a fixed support for said member intermediate to the ends thereof, said second contact being secured intermediate to the ends of the second section, a second slot in said member forming a third section, a second fixed support for said member intermediate to the ends thereof, the ends of said member being free to move as said contact moves from engaged to disengaged position whereby said contact movement is in a straight line and the length of the memher from said contact along said member to said support remains constant.

5. In combination, a first contact, a second contact movable into and out of engagement with said first contact, biasing means for biasing said second contact, a drive unit to drive said second contact against the action of said biasing means, and means for guiding said second contact in substantially a straight line from its engaged to its disengaged position, comprising a single fibrous member carrying said movable contact and having a first and second fixed supporting means and free end portions which are free to move as said contact moves, each of the fibres remaining substantially uneifected by the destruction of any other fibre.

6. In combination, a first contact, a second contact movable into and out of engagement with said first contact, biasing means for biasing said second contact into engagement with said first contact, means for operating said second contact out of engagement with said first contact against the action of said biasing means, a member, said contact and said member being secured to each other, a plurality of fixed supports, for said member symmetrically located with respect to said contact on the two 90 axes in the plane of said member and a plurality of slots, each of said slots substantially enclosing an individual support for mechanically isolating said contact carrying portion of said member and the edges of the member from said fixed support to permit the edges of said member to move as said contact moves and to permit substantial freedom of movement of said contact and edges of said member with respect to said fixed support.

7. In combination, a first contact, a second contact movable into and out of engagement with said first con tact, biasing means for biasing said second contact into engagement with said first contact, means for operating said second contact out of engagement with said first contact against the action of said biasing means, a member, said contact and said member being secured to each other, a plurality of fixed supports, adjacent the corners of said member, for said member symmetrically located with respect to said contact on the two 90 axes of the plane of said member and a plurality of slots, each of said slots extending from a position adjacent said contact in opposite directions and surrounding an individual support for mechanically isolating said contact carrying portion of said member and the edges of the member from said fixed support to permit the edges of said member to move as said contact moves and to permit substantial freedom of movement of said contact and edges of said member with respect to said fixed support.

8. A guide member for an oscillating unit, said guide member having a moving point to which said oscillating unit is secured, said guide member being mounted at various points which remain stationary during the oscillatory movement of said oscillating unit, elongated slots in said guide member, said elongated slots interposed in the area between said moving point and said stationary points, said guide member being symmetrical about both of its axes.

9. A guide member for an oscillating unit, said guide member having a moving point to which said oscillating unit is secured, said guide member being mounted. at various points which remain stationary during the oscillatory movement of said oscillating unit, elongated slots in said guide member, said guide member having a bending point as said oscillating unit is moved through a complete cycle, the distance between said moving point and stationary points being less than the distance from said moving point to said bending point, said guide member being symmetrical about the axes in the plane of said guide member.

10. A guide member for an oscillating unit, said guide member having a moving point to which said oscillating unit is secured, said guide member being mounted at various points which remain stationary during the oscillatory movement of said oscillating unit, elongated slots in said guide member, said elongated slots interposed in the area between said moving point and said stationary point, said guide member being symmetrical and identical about both the vertical and horizontal axes in the plane of said guide member.

11. A guide member for an oscillating unit, said guide member having a moving point to which said oscillating unit is secured, said guide member being mounted at various points which remain stationary during the oscillatory movement of said oscillating unit, elongated slots in said guide member, said guide member having a bending point as said oscillating unit is moved through a complete cycle, the distance between said moving point and said stationary point being less than the distance from said moving point to said bending point, said guide member being symmetrical and identical about both the vertical and horizontal axes in the plane of said guide member.

12. In a mechanical rectifier having a bridging contact and a pair of stationary contacts, biasing means to maintain said bridging Contact in electrical engagement With said stationary contacts, a push rod assembly to move said bridging contact against said biasing means to thereby disengage said bridging contact from said stationary contact, a guide member for said bridging contact, said bridging contact secured to said guide member at a first point, said guide member permanently secured at a plurality of stationary points, a plurality of slots in said guide member, one of said slots interposed in a direction substantially perpendicular to a line between said first point and one of said stationary points, said guide member being symmetrical and identical about two axes extending perpendicular to each other and in the plane of said guide member.

References Cited in the file of this patent UNITED STATES PATENTS 

